How to perfectly copy uv texture to another side without having to make them overlap?
I'm assuming you are using a newer version of Blender. I tested the following with Blender 2.90.1.
I used the setup below to demonstrate.

First you might want to copy your object. On the copy use overlapping UVs. In my case i mirrored the cube.

Then add another UV map to the object.
Next copy the old UVs to that map. You can do that by selecting both objects and press Ctr+L and choose &quot;Transfer UV Maps&quot;. (Select initial object last, thats where the UVs are coming from). You now have you target and source UV layout on the same object.
Next go to the Texture Paint mode and choose the clone brush. Set the Mode to &quot;Single Image&quot;
Create an empty texture and choose the destination UV layout. Also tick &quot;Clone from Paint Slot&quot;. Than choose your original texture map and one field underneath choose the original UV map.

Now draw over the mesh. you should see the texture beeing transfered from the original UVs to the new UVs. = )